AC Output Voltage Research Articles

A nonlinear optimal control approach for shipboard AC/DC microgrids

Shipboard AC/DC microgrids are used for power supply and electric propulsion in vessels. An indicative form of such a microgrid comprises diesel engines or gas turbines that provide power for the rotation of synchronous or asynchronous generators. Next, the AC output voltage of the generators is turned into DC voltage with the use of AC to DC converters and is distributed through DC voltage buses to the ship’s compartments. Besides, with the use of DC to AC inverters voltage excitation is provided to synchronous or asynchronous motors which can be used in turn for the vessel’s propulsion. The dynamic model of the considered shipboard AC/DC microgrid, being initially expressed in a nonlinear and multivariable state-space form, undergoes approximate linearization around a temporary operating point that is recomputed at each time-step of the control method. The linearization relies on first-order Taylor series expansion and on the computation of the associated Jacobian matrices. For the linearized state-space model of the shipboard AC/DC microgrid a stabilizing optimal (H-infinity) feedback controller is designed. This controller stands for the solution to the nonlinear optimal control problem of the AC/DC microgrid under model uncertainty and external perturbations. To compute the controller’s feedback gains an algebraic Riccati equation is repetitively solved at each iteration of the control algorithm. The global stability properties of the control method are proven through Lyapunov analysis. Finally, to implement state estimation-based control of the shipboard AC/DC microgrid, without the need to measure its entire state vector, the H-infinity Kalman Filter is used as a robust state estimator. The article’s method provides one of the few algorithmically simple and computationally efficient solutions for the nonlinear optimal control problem of shipboard microgrids.

3-Phase multi-inverter with cascaded H-bridge inverter designing and implementation for renewable system

Several applications of Distributed Generation networks uses Multilevel inverters, specifically photo voltaicsystems. Few major benefits of the Multilevel inverters are its power quality and the output voltages generated from the small PV voltage sources are high.Furthermore, AC output voltage is low for these inverters and it is nearly 400 V (phase to phase voltage). This research developed a compact three-phase modular multilevel inverter with symmetrical decomposition and asymmetrical of input multi-terminal for various PV system’s ratings. The 3-phase inverter proposed uses lower number of components. The design incorporates multiple carrier PWM for reduction of THD. The PV panels are related at every 3 phase VSI (Voltage Source inverter’s) DC side. The 3-phase isolation transformer with primary open-end windings, connects 3-phase VSIs AC sides in which multilevel operation are ensured. Three half-bridge cells for each phase for 7-level output voltage generation are combined. Proposed inverter is evaluated by comparing with existing methods such as Neutral-Point-Clampedthree-phase Multi Level Inverter (NPC-MLI), Multi Level Inverter with Linear Discriminate Notation Reactor (MLI with LDNR) and Cascaded H-bridge Multi Level Inverter (CHBMLI). Hence the proposed TPM-CHI achieves 2.1 V and 2.2amps of THD under symmetric disposition, 2.2 V and 2.4amps of THD under asymmetric disposition.

Nine-level Cascaded H-Bridge Multilevel Inverter for Photovoltaic Sources Based on Hybrid Active Filter

Nowadays, a multilevel inverter is one of the important devices that provides a practical approach device in power system industries because of its features which are less switching losses, lower electromagnetic interference, reduced harmonic distortion, higher DC link voltages, and improved output voltage and current waveforms. Among all existed multilevel inverter, cascaded H-bridge multilevel inverter is the most attractive because of the technology development with megawatt power level. So, the cascaded H-bridge multilevel inverter has been tested and proven as a suitable DC/AC device for medium and high power applications such as renewable energy systems, electric vehicles, and motor drive applications. In this paper, the project is focusing on the combination of a nine-level cascaded H-bridge multilevel inverter connected to photovoltaic (PV) sources and a hybrid powerfilter. This project aims to study and to analyze the results of the proposed system. Thebehaviour and the performance of the designed system have shown that the system offered330V peak output AC voltage with an efficiency of 93.96% and a 5% reduction of THD.This project will be carried out only in Matlab/Simulink software.

An Improved Multicarrier PWM (MCPWM) Technique With a New Harmonic Mitigation Strategy for Cascaded H-Bridge Multilevel Inverter Applications

The conventional modulation schemes of the cascaded H-bridge dc/ac converter generate a higher percentage of low-frequency harmonics at the output voltage and lead to discontinuous high-peak output current that causes a detrimental effect on the industrial motor drive systems. Addressing this concern, this article proposes an improved multicarrier pulsewidth modulation (MCPWM) technique that reduces harmonic content from the ac output voltage while achieving continuous output current with reduced peak magnitude. The proposed technique introduces a harmonic mitigation algorithm that adopts the switching angles of the MCPWM pulse to support the online adjustment of the modulation index and the switching frequency of the semiconductor switches. The main emphasis of this research is to mitigate the fifth, seventh, and eleventh order harmonics from the inverter output voltage and to define a new range of switching angles where the respective harmonics exhibit the lowest amplitude. Moreover, the work offers a novel approach to estimate the switching angles of the MCPWM pulse-train in real-time operation without solving the complex nonlinear equations. The proposed modulation technique has the benefits of low-frequency harmonic mitigation, low-processing time, and requirement of a minor segment of medium-sized FPGA, thereby it provides a good tradeoff between complex design and better performance. The feasibility and effectiveness of the proposed technique have been identified by a comprehensive comparison with the recently-reported schemes. Furthermore, theoretical, simulation, and experimental results using an FPGA-based three-phase cascaded H-bridge multilevel inverter prototype are included to justify the suitability of the proposed technique.

Non‐isolated high step‐up DC/DC converter for low‐voltage distributed power systems based on the quadratic boost converter

AbstractDistributed energy resources have been broadly developed in recent years for supporting DC and AC microgrids. Unfortunately, most of them produce low output DC or AC voltages, and interfacing converters are required. These are implemented either in single‐stage or dual‐stage configurations. Step‐up converters are the essential section in dual‐stage designs, which their producing gain is important. Improving the boost factor and efficiency as well as decreasing the number of required components and electrical stresses on power components are the most critical challenges in designing such topologies. Continuing past efforts, this paper proposes a new non‐isolated step‐up DC/DC converter that can be used in low‐voltage distributed power systems and many other applications requiring step‐up DC/DC conversion. The topology requires only one power switch located on the converter's low voltage (LV) side. Hence, it can be easily selected from LV ratings, low on‐resistance power semiconductors. Besides, the converter operates with a continuous input current, which is a valuable feature in connection with current‐sensitive voltage resources. Compared with the recently proposed topologies, the topology provides better conversion gain and efficiency. In this article, the operating principle of the introduced converter is comprehensively investigated. Also, in order to examine the converter performance, experimental results will be presented and analyzed. For this purpose, a 400 V/400 W prototype has been designed and built. Results confirm the above claims and show that the converter efficiency equals 96.1%, and it produces high output voltage gain about 12 times.

Solar Photovoltaic System-Based Reduced Switch Multilevel Inverter for Improved Power Quality

This paper deals with a reduced switch multi-level inverter for the solar photovoltaic system-based 127-level multi-level inverter. The proposed technique uses the minimum number of switches to achieve the maximum steps in staircase AC output voltage when compared to the flying capacitor multi-level inverter, cascaded type multilevel inverter and diode clamped multi-level inverter. The use of a minimum number of switches decreases the cost of the system. To eliminate the switching losses, in this topology a square wave switch is used instead of pulse width modulation. Thereby the total harmonic distortion (THD) and harmonics have been reduced in the pulsating AC output voltage waveform. The performance of 127-level MLI is compared with 15 level, 31-level and 63-level multilevel inverters. The outcomes of the solar photovoltaic system-based 127-level multi-level inverter have been simulated in a MATLAB R2009b environment.

An extended boost diode-clamped impedance source inverter for electrical vehicle powertrain motor drive

Improving Electric Vehicle motor drive fast charging and discharging analysis use extended boost Diode-Clamped Z- source Impedance Inverter. A single–stage power conversion by using unique impedance (Z) network with inverter circuit to boost AC output voltage through shoot-through (ST) and non-ST. In this case, Z networks are directly responsible for balancing the inductive voltage boosting and output levels. The ST states limit the modulation index and cause huge ST current in the inverter phase legs.The conventional Pulse Width Modulation (PWM) methods for Z-source Neutral Point Clamped (NPC)-Multi Level Inverter (MLI) use the full ST (turned ON all the inverter switches in a leg), which occupies more switching commutations per switching cycle and leads to unequal inductor charging and discharging, resulting in more harmonics in the output voltage and current waveforms. It is noted from earlier developmental drifts that by using a single Z-network, performance dreadful conditions are usually expected. Creating the full ST misguides to extra switching commutations as well as unequal charging and discharging of inductor. The proposed Z-source MLI (Space Vector Modulation) SVM technique offers a Top and Bottom ST for charging the Z-network inductors with balance the inverter DC-link capacitor. The simple mathematical function used based on two-level SVM Z-source MLI SVM proposed and has more flexibility to choosing the switching patterns without complex function; thereby it offered real time implementation in simpler manner. The also paper contributes a comprehensive study on development procedure of proposed Z-source MLI SVM FPGA environment validation. The proposed SVM is implemented with three-level Z source neutral point MLI through MATLAB simulation and 1-kW experiment prototype is built to verify the theoretical analysis.

Optimized piezoelectric energy harvesting circuit using DC/DC converter

Some electrical devices, such as those harvesting energy from vibrations, deliver an AC output voltage that needs to be rectified. A DC / DC conversion stage is, in most situations, necessary for correct management of the recovered energy. This type of circuit makes it possible to raise or lower the voltage delivered by the generator. To some extent to match the impedance. The impedance match plays an essential role in the performance of the transducer, given that its optimum operating point can vary over time, and deviating from this optimum point can rapidly drop the harvested power.Many approaches proposed in the literature are based on switching converters. The operation of these converters is based on the switching of the current between storage elements, inductors and capacitors. The converters step-down or step-up, these have the advantage of allowing the adjustment of the ratio between output voltage and input voltage, which results in a controllable input impedance.In this study, we propose an architecture associating a rectifier and a Buck converter, allowing charging a battery from a piezoelectric transducer. The measurement of the battery charging current is used to define the duty cycle that maximizes the energy harvested. In this case, the DC/DC down converter is appropriate because the transducer provides a voltage higher than 45 V in open circuit, while the considered power range is from 1 to 120 mW. The authors show a 415% improvement in the recovered power, compared to the case of a direct load.

Active Switched-Capacitor Embedded Quasi-Z-Source Inverter and PWM Methods for High Boost Capability and Switching Loss Reduction

This paper proposes a novel topology, named a single-phase active switched-capacitor embedded quasi-Z-source inverter (ASC-EqZSI), and two pulse-width modulation (PWM) methods, namely, PWM1 and PWM2 methods for the proposed ASC-EqZSI topology to improve the boost capability and reduce switching loss. The boost capability can be improved by using an additional non-shoot-through (NST) state, referred to as the NST2 state, besides conventional shoot-through (ST) and NST states. In the NST2 state, the switch in the impedance network is switched on to boost the dc-link voltage while generating the ac output voltage. A PWM1 method is suggested to control both the NST2 and ST time intervals with one carrier signal for improving the boost capability. A PWM2 method aims to reduce the commutation count of the switches and diodes in the proposed topology while maintaining the enhanced boost capability. The switching loss can be reduced by almost 40%. A comparative analysis between the proposed topology with the PWM2 method and five other topologies with an active switched Z-network is performed. The proposed topology with the PWM2 method has a higher ac voltage gain and efficiency with fewer components. Simulation and experimental results are carried out to validate the performances of the proposed topology and PWM methods.

A 3-Ф grid connected wind system with a technique of DC link control using fewer sensors with fuzzy controller

PurposeThis paper aims to provide a permanent magnet synchronous generator (PMSG) wind turbine, which feeds electric power (AC) to the power grid. The converter, located on the machine side, is used to produce the full amount of wind power. Research on wind energy conversion system (WECS) is carried out in this study using a direct wind turbine in MATLAB with constant and variable speeds.Design/methodology/approachThis paper is about WECS using PMSG and is connected to a grid of two serial converters with common DC connections.FindingsThis paper aims to provide the value of DC connection voltage at its base, regardless of the wind speed alterations, the inverter's output ac voltage can be kept constant.Originality/valueThis paper aims to provide a Hill Climb Search maximum power point tracking (MPPT) algorithm is an effective control system for extracting maximum energy, also called voltage control, pitch control, phase-locked loop (PLL) controls, from a wind turbine. Using the Fuzzy controller, the grid side converter is controlled.

Performance Analysis of Z-Source Inverter Control Techniques

This study presents the different control techniques of the Z-Source inverter (ZSI) and compares them for the same modulation index. Different from the traditional inverters, in ZSI circuit configurations simple boost, maximum boost, and maximum constant boost control techniques can be utilized to perform DC-AC voltage conversion with shoot-through states. The operation principles of the control techniques are explained in detail. The shoot-through duty ratio, the boost factor, and the voltage gain for each control technique of the ZSI are calculated using the related equations. The ZSI circuit model and the simulations of the DC-link and the AC output voltage are performed in Matlab/Simulink environment. According to the related equations used in the different control techniques and the obtained simulation results, the maximum boost control technique has the highest boost factor and voltage gain for a determined modulation index. For that reason, the maximum boost control technique has the maximum equivalent DC-link voltage and AC output voltage under the same conditions. This control technique can be employed for inverter applications where the highest gain is required.

Measurement-based extrapolation of spectral responsivity by using a low-NEP pyroelectric detector

In case the primary realization of the spectral responsivity scale is not conducted at all target wavelengths but at only a small part of them, one needs to extrapolate values at the specific wavelengths to an extended range. In this work, we present a fully experimental procedure to extrapolate a single value of spectral responsivity at 633 nm into the whole working wavelength range (250–1100) nm of Si photodiodes. It is based on spectral responsivity comparison between a Si trap detector and a low-noise equivalent power pyroelectric detector of nearly flat spectral response. For this purpose, we developed a setup specialized to compare a Si-trap detector of dc-current output with a pyroelectric detector of ac-voltage output by using a modulated probing light source and a monitoring technique. To keep the probing light chopped even for the dc-photocurrent readout, we adopted a low chopping frequency of 4 Hz and a triggered readout for the Si-trap detector, which leads to a speedy comparison between the Si-trap detector and the pyroelectric detector. For the reference pyroelectric detector, we characterized the spectral absorptivity of the black-coating and the nonlinearity of the lock-in amplifier readout. Compiling all the required information, the spectral responsivity of the Si trap detector could be measured with the minimum uncertainty of 0.3% (k = 2), which was validated by comparing with that of our previous method based on a numerical extrapolation.

Improvement Approach for Matching PV-array and Inverter of Grid Connected PV Systems Verified by a Case Study

Correct matching between PV array and inverter improves the inverter efficiency, increases the annual produced energy, decreases the clipping losses of the inverter, and prevent to a large extent the inverter frequent shut downs during clear sunny days of high solar radiation and low ambient temperature. Therefore, this paper presents a new methodology for selecting the appropriate peak power of the PV array with respect to the inverter output AC rated power taking into account the local daily distribution of solar radiation and ambient temperature. In addition, the proposed methodology specifies the appropriate number of PV modules in each string and the number of parallel strings connected to the input of the inverteraccording to its specifications and to PV cell temperature. Mathematically modeling of system parameters and components are presented and used in the simulation to investigate the different scenarios. The paper presents also a case study using simulation to find the optimal matching parameters of a PV array connected to an inverter with the specifications: 6 kW rated output power, an input mpp voltage range of 333-500 V, 6.2 kW maximum input DC power, and an output AC voltage of 230 Vrms. Considering the local climate conditions in West Bank, the simulation resulted a peak power of 7 kW for the PV array, which is greater than the inverter output power by the factor 1.16. In addition, the obtained PV array consists of two parallel strings each includes 12 PV modules connected in series while each PV module is rated at 290 W. The output voltage of the PV arrayvaries between 359 V to 564 Vat minimum and maximum temperature of 10 ˚C to 70 ˚C respectively. This PV array-inverter combination resulted by simulation an annual yield of 1600 kWh/kWp and an energy of 11197 kWh which corresponds to an energy gain of 1591 kWh/year more than using a PV array with a peak power of 6 kW as the inverter rated power.

Experimental Research on Wind-Induced Flag-Swing Piezoelectric Energy Harvesters

Piezoelectric cantilever beams, which have simple structures and excellent mechanical/electrical coupling characteristics, are widely applied in energy harvesting. When the piezoelectric cantilever beam is in a wind field, we should consider not only the influence of the wind field on piezoelectric beam but also the electromechanical coupling effect on it. In this paper, we design and test a wind-induced flag-swing piezoelectric energy harvester (PEH). The piezoelectric cantilever beam may vibrate in the wind field by affixing a flexible ribbon to the free end as the windward structure. To fulfill the goal of producing electricity, the flexible ribbon can swing the piezoelectric cantilever in a wind-induced unstable condition. The experimental findings demonstrate that the flag-swing PEH performs well in energy harvesting when the wind field is excited. When the wind speed is 15 m/s, the peak-to-peak output AC voltage may reach 13.88 V. In addition, the voltage at both ends of the closed-loop circuit’s external resistance is examined. The maximum electric power of the PEH may reach 43.4 μW with an external resistance of 650 kΩ. After passing through the AC-DC conversion circuit, the flag-swing PEH has a steady DC voltage output of 1.67 V. The proposed energy harvester transforms wind energy from a wind farm into electrical energy for supply to low-power electronic devices, allowing for the creation and use of green energy to efficiently address the issue of inadequate energy.

Isolated DC–DC Boost Converter for Wide Input Voltage Range and Wide Load Range Applications

A current-fed dual-inductor resonant full-bridge dc–dc isolated boost converter is proposed. The converter is most suitable for applications that demand wide input voltage and load ranges. It can be used as a front-end dc–dc converter that can boost variable low voltage from a power source [battery (home/industrial inverter/industrial UPS application), fuel-cell, or solar-PV] and interface it to a high-voltage dc-link, which typically feeds an inverter. It removes all major drawbacks of conventional current-fed isolated dc–dc converters, namely high-voltage spikes across the switches due to transformer leakage inductance, need for additional start-up circuit, and difficulty in converter tripping in case of faults. Soft-switching of rectifier didoes and clamping power switches is load independent leading to good efficiency over entire load range. Converter can be operated with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> < 0.5, making it suitable for wide input voltage range applications. A detailed comparative analysis with state-of-the-art converters for wide input voltage range applications considering the major important factors, such as power device utilization, transformer utilization, inductive energy requirement, and dc capacitors utilization, confirms the superiority of the proposed converter. Experimental results for a 2.5 kVA inverter application with an input dc voltage range of 90–160 V and output ac voltage of 230 V are provided.

Buck and Boost Inverter

Abstract: A versatile operation of any electronic circuitry depends on the power source supplying the power for its operation. The buck converter is implemented using an integrated circuit(IC), LM317. The constructed buck converter was tested for load and line regulation cited in the datasheets for stability. The test and analysis for the linear buck converter was done using setup. The output measurements indicate that the power supply is functional. The measured output values results of the test circuit. The developed output power supply unit is important in measurements, laboratories and test setup. It is implemented for all general applications that require power supply unit. XL6009 module is a DC to DC BUCK-BOOST converter module that operates at a switching frequency of 400kHz. In such high frequency, it provides smaller sized filter components compared with low frequency switching regulators. An improved SingleStage Buck-Boost inverter is provided, using only three or four power semiconductor switches. The inverter can handle a wide range of dc input voltages and produce a fixed ac output voltage. The inverter is well suited to distributed power generation systems such as photovoltaic and wind power and fuel cells, for standalone or grid connected applications. The inverter has a single charge loop, a positive discharge loop and a negative discharge loop. In this complete design of the converter is carried out. This application report gives details regarding this conversion with examples

PERFORMANCE EVALUATION OF VOLTAGE RECTIFIERS FOR ENERGY HARVESTING APPLICATIONS

Voltage multipliers are used to convert the low AC voltage output of energy harvesters into relatively high DC voltage for portable devices and wireless sensor nodes (WSNs) applications. DC voltage conversion is required to operate an electronic device or recharge battery. In order, to convert the low AC voltage output of the energy harvester into relatively high DC voltage, a voltage multiplier circuit need to be integrated with the energy harvester. In this study, a Prototype-1 (two-stages) and Prototype-2 (three-stage) Dickson voltage multipliers and Prototype-3 (seven-stage) Cockcroft-Walton voltage multiplier circuits are developed. The device is capable of converting a low voltage of 50 mV into 350 mV. The research focuses on the development and characterization of Prototype-1, Prototype-2 and Prototype-3 circuits. Results indicate that the determination of load resistance is important for better output power. The maximum power of 11.97 μW was obtained by prototype-3 elucidating better power compared to prototype-1 and prototype-2 and the power was obtained at an optimum load of 560 kΩ. Furthermore, a rectenna tested at different distances from the source, revealed that a prototype-2 produced a maximum power of 3.01 × 10 -6 μW, at an optimum load of 560 kΩ.

A dynamic equivalent aggregation method of wind turbine systems with a full‐scale power converter for electromagnetic transient simulations

With the increasing exploitation of wind energy, the dynamic performances of large-scale wind farms (WFs) are vital for the system design and stability analysis. However, a detailed WF model considering every wind turbine system (WTS) makes the electromagnetic transient simulation time-consuming and computational-demanding. Therefore, a dynamic equivalent aggregation method is proposed for WTS with a full-scale power converter (WTS-FSPC) in this paper, in order to reduce the computational complexity meanwhile maintaining the same accuracy as the detailed model. To improve the accuracy of the equivalent collector system, the collecting strings are decoupled based on the power flow distribution. Then the WTSs are clustered according to the output AC voltage distributions using a Louvain K-means (LKM) algorithm, which innovatively determines the optimal solution automatically. Additionally, a centralized capacitor is set to represent the distributed capacitance of the collector system. Furthermore, to enhance the model adaptability during asymmetric short-circuit faults, the equivalent method for the zero-sequence collector system is introduced. Time-domain simulation results demonstrate the effectiveness and robustness of the proposed method in reflecting the WF dynamics. The case study in a 2-area system further verifies the superiority of the proposed method for the WF integrated power system stability analysis.

Performance Comparison Modeling Between Single-phase Cycloconverters and Three-phase Cycloconverters Using Matlab Simulink Tools

This paper presents a performance comparison of a single-phase AC to AC converter (cycloconverter) and a three-phase converter circuit which divides the input wave frequency (fin) into a variable frequency with the frequency value of the AC output voltage waveform (alternating current) (f, fin/2, fin/3, fin/4, fin/5, fin/6, fin/7, fin/8, fin/9, fin/10. Cycloconvertor switches are built using a diode and a thyristor device. This research was conducted by modeling each cycloconverter circuit using Matlab Simulink tools. Modeling simulation parameters to be analyzed include the output waveform RMS (root mean square) value, frequency value, and Total Harmonic Distortion (THD) index for each wave. The output frequency voltage waveform of cycloconverter is affected by the variation of the trigger signal of the P-side (positive) converter and the N (negative) converter side switch. Simulation results show that adjusting the firing pulse width of the P converter and the N converter will produce an output voltage wave that has an index value of THD, Vrms, and form factor for each diode and thyristor cycloconverter circuit.

Comprehensive review of single stage switched boost inverter structures

Single-stage switched boost inverter (SBI) with buck-boost capability finds wide applications in renewable energy systems (RES). This paper aims at a comprehensive topological review of various single stage SBI circuits. The boosting techniques of SBI include switched inductor, switched capacitor, and transformer assisted switches. Each SBI derived structure has its own merits and demerits depending on the applications. The performance evaluation of SBIs, based on various perspectives like boost factor, voltage stress across active devices, passive elements count, DC link voltage, switching losses, voltage gain, and efficiency, are also discussed. A suitable modulation strategy is used to obtain the desired boosted and inverted ac output voltage in one stage SBI. Different modulation strategies adopted for SBIs are also included at the end of the topological review. This topological review's contribution enlightens the researchers in selecting appropriate SBI with effective modulation strategies suitable for renewable energy applications. Besides, the benefits and shortcomings of these converters are discussed in detail.